1. Field of the Invention
The present invention relates to an antenna and a complex antenna, and more particularly, to an antenna and a complex antenna having smaller size to be disposed in a cylindrical radome and allowing both multiband and low-frequency operations.
2. Description of the Prior Art
Electronic products with wireless communication functionalities utilize antennas to emit and receive radio waves, to transmit or exchange radio signals, so as to access a wireless communication network. With the advance of wireless communication technology, an electronic product may be configured with an increasing number of antennas. Alternatively, a complex antenna equipped with a plurality of antennas may be used in an electronic product to transmit or receive radio signals. A complex antenna turns on its antenna (s) according to the direction of signal transmission, thereby effectively enhancing spectral efficiency and transmission rate for the wireless communication system, as well as improving communication quality. In such a situation, each of the antennas constituting a complex antenna is preferably a directional antenna, which point energy toward a specific direction for concentration within a targeted area.
An ideal antenna should maximize its bandwidth within a permitted range, while minimizing physical dimensions to accommodate the trend for smaller-sized electronic products. Technically, a complex antenna is disposed in a cylindrical radome, which limits the sizes of the antennas constituting the complex antenna. However, the long term evolution (LTE) wireless communication system includes 44 bands which cover from 698 MHz to 3800 MHz. Because of the bands being separated and disordered, a mobile system operator may use multiple bands simultaneously in the same country or area. In the LTE wireless communication system, band 13 (covering from 746 MHz to 787 MHz) requires lower frequencies, and hence a complex antenna operated in band 13 would occupy larger space. Without adequate size, the complex antenna cannot meet the requirements of multiband or wideband transmission. What's worse, interference between antennas might occur to threaten normal operations of the antennas.
Obviously, providing an antenna of small size that allows multiband and low-frequency operations is a significant objective in the field.